This invention relates generally to methods and apparatus for providing precisely measured amounts of granular materials preparatory to further processing of the combined granular materials and specifically to gravimetric blenders providing precisely measured amounts of plastic resin material and mixing these components prior to supplying the blended mixture to plastics manufacturing and processing equipment such as plastic injection molding, compression molding and extrusion equipment.
The modern gravimetric blender was essentially originated by the applicant of this invention and is widely used throughout the world by industries concerned with precision feeding of granular material, especially plastic resin material.
Gravimetric blenders operate by blending solid plastic resin material components and additives, by weight, in batches.
Typically batches of material may consist of several solid material components. One of these may be xe2x80x9cregrindxe2x80x9d, consisting of ground plastic resin which had previously been molded or extruded and which either resulted in a defective product or was excess material not formed into a desired product.
Another component may be xe2x80x9cnaturalxe2x80x9d plastic resin which is virgin in nature in the sense that it has not previously been processed into a molded or extruded plastic part.
Yet another component may be a solid color material, typically flakes or freeze dried material, used to produce a desired color of the finished plastic part.
Still yet another component may be an additive used to adjust the blend to provide required performance characteristics during molding, extrusion or subsequent processing.
The gravimetric blender as originated by the applicant and as copied widely throughout the world typically includes hoppers for each of the components of the solid material to be blended together. Typically several hoppers or several compartments in a hopper may be provided, such as one compartment for xe2x80x9cregrindxe2x80x9d material, one compartment for xe2x80x9cnaturalxe2x80x9d material, one component for solid color additive material and one compartment for xe2x80x9cadditivexe2x80x9d.
When the gravimetric blender operates, the unit desirably operates automatically, adding each of the component solid materials in the proper, desired percentages. Each solid material component is dispensed by weight into a single weigh bin. Once the proper amounts of each component have been serially dispensed into the weigh bin, all of the components are dropped together into a mixing chamber from the weigh bin.
Mixing is performed, preferably continuously, and preferably even as additional batches component are dispensed in the mixing chamber. When mixing is complete, the resulting blend is preferably provided directly to the desired molding or extrusion machine.
Feedback control of the dispensed amounts of each solid material component provided to the weigh bin and measured by weight assures that in the event of an error in the amount of a dispensed component, the succeeding batch may have the blend adjusted to account for the error detected in the preceding batch of blended material.
As one of the components forming a part of the resulting blend it is known to supply solid color additives to the blend in order to provide a blend of a desired color. These color additives may be flaked pigments on wax carriers or in freeze dried form. It is also known to provide the color as pigment powder constituting one component of the resulting blend.
In one of its aspects this invention provides a gravimetric blender including a frame, a material storage hopper removably mounted on the frame, valve means proximate the hopper bottom for dispensing material within the hopper, and means connected to the hopper and remaining so upon removal of the hopper from the frame, for actuating the valve means to downwardly dispense material within the hopper, a weigh bin connected to the frame below the hopper, means connected to the frame for sensing weight of material in the bin, and a mix chamber below the weigh bin.
Desirably, the means for actuating the valve is fixedly connected to the hopper, the actuating means is at least partially within the hopper, the valve means is at least partially within the hopper, the hopper is manually removable from the frame, and it further includes a plurality of hoppers, each with valve means therewithin and respective individual valve actuation means. The actuating means is pneumatically driven and includes a vertically elongated member for transmitting motion to the valve.
The gravimetric blender includes a frame, a weigh bin, means connected to the frame for sensing weight of material in the bin, a mix chamber below the bin and connected to the frame, means connected to the frame for selectably contacting and opening the bin to release material in the bin downwardly into the mix chamber. The blender further preferably includes means for biasing an openable portion of the bin towards a closed position; the openable portion is preferably movable about a pivot; the openable portion preferably pivots about a horizontal axis; the means for selectably contacting and opening the bin is preferably pneumatically actuated; the means for selectably contacting and opening the bin is preferably a piston-cylinder combination; the cylinder is preferably outward of the frame; the piston preferably moves transversely to the axis about which the openable portion pivots; the piston may contact the bin directly or indirectly; the openable portion is preferably pivotally connected to a remaining, stationary portion of the bin.
The piston is preferably disconnected from the bin when the movable portion is at the closed position.
The invention further includes means for selectably contacting and opening the bin.